Nervous system Flashcards
What are the parts of the nervous system?
Central and peripheral
Describe the central nervous system:
- Made up of the brain and spinal cord
- Integrates and processes information
Describe the peripheral nervous system:
- Peripheral nerves
- Carry messages to and from the central nervous
system
What is the somatic nervous system?
- Voluntary control
- Connects to skeletal muscles
- Part of peripheral nervous system
What is the autonomic nervous system?
- Involuntary control
- Connects to smooth muscles and glands, internal organs
- Part of peripheral nervous system
What are the two divisions of the autonomic nervous system?
Sympathetic and parasympathetic
What is a sympathetic response?
Fight or flight
What is a parasympathetic response?
Associated with rest
Describe neurons:
- Basic structural and functional unit
- Respond to physical and chemical stimuli
- Conduct electrochemical signals
- Release chemicals that regulate body processes
- Sometimes very long
What are glial cells?
- Support neurons by
- Nourish neurons, remove wastes, immune defence, supporting framework
- About ½ the volume of the nervous system
- Outnumber neurons 10 to 1
What are nerves?
- Bundles of neurons
- Surrounded by protective connective tissue
- Carry messages/signals throughout the body
What are the three types of neurons?
Sensory, interneurons, motor
What do sensory neurons do?
Gather info from sensory receptors and transmit impulses to CNS
What are interneurons?
- Found in the CNS
- Link between sensory and motor neurons
What do motor neurons do?
Transmit information from CNS to muscles, glands and organs (effectors)
Draw the nerve impulse pathway:
effectors <—— motor neurons <—– Interneurons <—– sensory neurons <—— Sensory receptors
What is a reflex?
- Used in emergency situations
- Sudden, involuntary response
What is a reflex arc?
- Simple connections of the neurons
- Very few neurons involved
- Signal to move effector comes directly from the interneurons in the CNS (brain or spinal cord)
- No voluntary control involved
- Also known as neural impluse pathway
What are the four basic parts of all neurons?
- Dendrites
- Cell boy (soma)
- Axon
- Branching ends
What are dendrites?
- Receive impulses/signals
- Short branches
What is the cell body?
- Contains nucleus
- Processes information from dendrite
- Signal only proceeds beyond the cell body if the signal is strong enough
- Contains metabolic reactions for cell
What is the axon?
- Only one
- Conducts impulses away from the cell body
- Vary greatly in length (1mm to 1 m)
What are the axon branches/terminal fibres?
- Chemical signals released from here
- Communicate with other nerves or effectors such as muscles
What is the myelin sheath?
- Fatty, insulating layer on some axons
- Protects neuron
increases speed of nerve impulse transmission - Formed by Schwann cells (a type of glial cell)
What are the nodes of Ranvier?
- Gaps in Myelin Sheath
- Where action potentials occur
What are the three basic stages to nerve transmission?
- Resting membrane potential - the relative charge inside of a resting neuron, contains potential energy
- Membrane depolarization - occurs when membrane is excited, this is when a stimulus is transmitted
- Membrane repolarization - the process of a neuron returning to resting membrane potential
Describe resting membrane potential:
- A neuron at rest is more negative inside than on the outside
- Caused by a greater concentration of positive ions outside the membrane of the neuron
- Charge separation is a form of potential energy “membrane potential”
- Approximately -70mv
Why is it is -70mv?
- Potential energy provides energy for generation of nerve impulse
- Larger number means a certain degree of stimulus is needed to create an impulse
Describe polarization:
- Process of generating resting membrane potential
- There is already a tendency for a neuron to be more negative inside because of:
- Large negative protein molecules in cell cannot get out
- Membrane nearly impermeable to some negative ions
- Very important contributor to the charge difference, as well as the way a neuron restores membrane potential is the sodium-potassium pump
- Potassium diffuses out of the cell faster than sodium diffuses in because of gated protein channels
What is the sodium-potassium pump?
- Uses ATP to transport sodium out and potassium into the cell
- Three sodium ions are pumped out for every two potassium pumped in
- Potassium ions diffuse out of the cell more easily than sodium ions diffuse in (because of gated channels for potassium)
- Result is more positive outside and more negative inside
Describe membrane depolarization:
- When the nerve cell is excited, the membrane depolarizes
- The membrane’s polarity changes, sodium channels open, sodium rushes in, potassium gates close
- The positive ions. flowing in causes a charge reversal to + 40 mv
- Once the charge becomes positive the sodium gates close, potassium gates open, eventually restoring the charge to -70mv (but the sodium and potassium excess is inside)
What is the threshold potential?
- Charge that must be reached before a
stimulus will result in a nerve impulse - About -55mv in most, but not all neurons
- Any change to less than -55mv (between -
70mv and -55mv) will have no effect - This is why a neuron response is
sometimes called “all or none”
What is action potential?
- Charge reached above threshold potential
- A nerve transmission begins or continues
Describe membrane repolarization:
- The Na+/K+ pump restores the ion
concentrations inside and outside the cell - During the repolarization, the nerve cannot
be reactivated – called the refractory
period (1 to 10 ms) – this is a recovery
time for the neuron - The pump requires ATP in order to
operate - K+ channels open and k+ flows out
Describe the movement of action potential:
- The action in the neuron adjacent to an area of resting membrane causes that area to depolarize, moving the action potential along ( due to attraction of opposite charges)
- Since the area from which the action potential came in is still in recovery, the action potential will only move in one direction
What can an action potential stronger response result from?
- Increased frequency of the neuronal firing is (not speed, which is constant for each neuron)
- The number of neurons that respond to that level of stimulus (neurons may have different thresholds)
What is the refractory period?
- Period after an action potential when a new impulse cannot be created
- Voltage gated sodium channels have not recovered and are not able to be opened at this point
What is the role of the myelin sheath in the nodes of ranvier?
- A nerve impulse travels much faster in a myelinated neuron
- The insulating properties of myelin mean action potential can only occur at the noded of ranvier
- Result is less membrane needs to go through depolarization
- Goes faster
Describe white vs. grey matter:
White matter - myelinated neurons
Grey matter - unmyelinated neurons
What does the peripheral nervous system do?
- Links brain and spinal cord to rest of body
- Sends sensory impulses to the CNS
- Transmits motor impulses from CNS to effectors
- Divided into somatic (voluntary) and autonomic (involuntary) systems
What is the somatic system?
- Voluntary control
- More spinal nerves than cranial nerves are all myelinated
What are the cranial nerves of somatic system?
- Mostly associated with functions of the head, neck and face
- Vagus nerve is cranial nerve that connects to internal organs
Describe the spinal nerves of the somatic system:
- 31 pairs
- Each nerve contains sensory and motor neurons
- Each nerve services the area of the body where it is found
What is the autonomic system?
- Involuntary control
- Nerves inhibit or stimulate glands, cardiac muscle or smooth muscle
- Maintains homeostasis
- Controlled mainly by hypothalamus and medulla oblongata
- Divided into sympathetic and parasympathetic
What is the sympathetic nervous system?
- Responsible for fight or flight response
- Sympathetic neurons release the neurotransmitter norepinephrine
- Also signal adrenal glands to release epinephrine and norepinephrine
What is norepinephrine?
- Excitatory effect on target muscles
- Acts with epinephrine to trigger stress response
What is the stress response?
- Increases heart rate and blood pressure
- Diverts blood to skeletal muscles
- Slows digestion
Describe the parasympathetic nervous system:
- Active when body is at rest
- Restores and conserves energy
- Reverse effect of stress response
- Main neurotransmitter involved in acetylcholine
Sympathetic and para sympathetic systems usually work to _______ one another (balance)
Counteract
What is grey matter?
- Contains mainly cell bodies, dendrites and short, unmyelinated axons
- Found around outside of brain and center of spinal cord
What is white matter?
- Contains tracts of myelinated axons
- Forms some inner areas of brain and outside of spinal cord
Describe the spinal cord:
- Column of nerve tissue that travels from brain down the spine
- Collects messages and sends them to brain
- Sends messages form brain to effectors
primary reflex center - contains interneurons of most reflex arcs - Centre contains grey matter
- Cell bodies and dendrites of spinal neurons
- Spinal cord is protected by vertebrate, soft tissue, meninges (a thick membrane) and cerebrospinal fluid
Describe the blood brain barrier in the brain:
- Formed by meninges (membrane around CNS) and tight-walled capillaries
- Keeps blood and nervous system separate
- Oxygen and lipid - soluble materials can get through
- Other toxins cannot
Describe the cerebrospinal fluid in the brain:
- Circulates through spaces and around the CNS
- About 500 ml/day produced
- 150ml in system at one time
- Transports hormons, white blood cells and nutrients across blood-brain barrier
- Shock absorber (cushions brain)
Describe oxygen and the brain:
- Brain makes up 2% of bodies weight
- Uses 20% of bodies oxygen
- Lack of oxygen for a few minutes can cause major brain damage
What is the structure of the brain?
- Mass of neutral tissue - grey matter outside and some white matter inside
- Gelatin - like consistency
- Surrounded by cerebrospinal fluid, menings and the skull
What are the sections of the brain?
Hindbrain, Midbrain, Forebrain
Describe the hindbrain:
- Cerebellum, medulla oblongata and pons
- Mostly control of involuntary responses such as posture and coughing
- Some fine motor voluntary control
What is the the midbrain?
- Small area in the center of the brain
- Relays messages between fore and hindbrain
- Key role in eye movement
Describe the forebrain:
- Thalamus, hypothalamus, cerebrum
- Thoughts, memory, language, emotions and some involuntary responses
Describe the cerebellum:
- Walnut shaped structure near the base of the brain
- Posture, some reflexes, involuntary movements
- Fine voluntary motor skills such as writing
- Receives information from “proprioceptors” - specialized sensors in muscles and joints
Describe the medulla oblongata:
- At base of brainstem
- Connects brain to spinal cord
- Automatic involuntary responses
- Heart rate
- Constriction and dilation of blood vessels
- Rate and depth of breathing
- Swallowing
- Digestion and vomiting
- Coughing
Describe the pons:
- Above and in front of medulla oblongata
- Relay center between right and left cerebrum, the cerebrum and rest of the brain
Describe the midbrain:
- Above pons
- Relays visual and auditory information between hindbrain and forebrain
- Role in eye movement and skeletal muscle control
Describe the cerebrum:
- Largest part (4/5 of the brain)
- Two hemispheres (right and left)
- Responsible for thoughts, memories, understanding, consciousness and language
- Convoluted to increase surface area
- Further divided into lobes
Describe the thalamus:
- Base of forebrain
- Connections between hind and forebrain
- Connections between senses (except smell) and cerebellum
Describe the hypothlamus:
- Just below thalamus
- Major link between nervous and endocrine systems
- Controls (mainly through hormone production):
- Blood pressure
- Heart rate
- Body temperature
- Thirst and hunger
- Emotions
Describe the corpus callosum:
- A bundle of white matter linking L and R hemisphere - Sends signals back and forth between halves
- In the cerebrum
Describe right vs left brain:
- Both halves of brain involved in cognitive processes
- Each side of brain is thought to have more of a role in certain functions
Describe the left brain:
- Sequential and logical thinking
- Linguistic skills
- Mathematical ability
Describe the right brain:
- Intuition
- Visual: spatial skills
- Artistic abilities
What is the cerebral cortex made of?
Four pairs of lobes
- Frontal
- Parietal
- Temporal
- Occipital
Describe the frontal lobe:
- Thought
- Intelligence
- Memory
- Personality
- Voluntary motor
Describe the parietal lobe:
- Process sensory information from skin
- Process information about body position
Describe the temporal lobe:
- Auditory reception
- Understanding speech
- Retrieving visual and auditory memories
- Process some visual information
Describe the occipital lobe:
- Receive and and process visual information
Define synapse:
Connections between neuron and effector
Define neuromuscular junction:
Synapse between motor neuron and muscle cell
Define synaptic cleft:
Gap between neurons (most of the are not connected directly)
Define neurotransmitter:
Chemical messengers that work between neurons
Define synaptic vesicle
Sac containing neurotransmitter
What happens when a signal reaches the end of an axon?
- Action potential causes synaptic vesicle containing neurotransmitter to fuse
- Neurotransmitter released into cleft by exocytosis
- Neurotransmitters diffuse across synapse and bind to special receptors on postsynaptic membrane
- Ion channels are signaled to open on postsynaptic membrane
- Enzymes break down neurotransmitter
What happens in the excitatory neurotransmitters?
- Sodium channels are triggered to open
- Nerve because depolarized
- If signal is strong enough, action potential is initiated
What happens in the inhibitory neurotransmitters?
- Signals potassium channels to open, potassium reaches out
- Neuron becomes hyperpolarized
What is the role of the cell body?
- Sometimes a neuron is receiving excitatory and inhibitory signals at the same time
- The cell body helps to sort through the information and send a signal (if strong enough) to the axon
What is an acetylcholine?
- Example of an excitatory neurotransmitter
- Excites muscle cell membrane
- Causes muscle contraction
- Broken down by the enzyme, cholinesterase
What are sensory receptors?
Nerve endings and cells that detect sensory information
Define sensation:
When nerve impulses arrive at cerebral cortex
Define perception:
Results from processing in the cerebrum
Describe sensory adaptation:
Brain filtering out information, usually as a result of constant exposure to that stimulus
What are the different sensory receptors?
- Photoreceptors - stimulated by light
- Chemoreceptors - stimulated by chemicals
- Mechanoreceptors - stimulated by pressure
- Thermoreceptors - stimulated my temperature
What is the eye?
- Hollow ball filled with fluid
- Allows us to see by focusing light on photoreceptors at the back
What are the layers of the eye?
- External: sclera and cornea
- Intermediate: choroid, iris, pupil, ciliary muscles
- Internal: retina
Describe the sclera:
Tough, white outer covering of eye
Describe the cornea:
Transparent area of sclera at front of eye (light enters here)
Describe the choroid:
- Intermediate layer
- Absorbs stray light waves
- Contains blood vessels that supply eye with nutrients and oxygen
Describe the iris:
Made of muscle that contracts or relaxes to allow different amounts of light in (adaptation)
Describe the pupil:
The “hole” in the centre of the eye where light gets through
Describe the coliseum muscle/lens:
Ciliary muscle adjusts lens to help focus light on retina
Describe the retina:
- Internal layer of the eye
- Contains photoreceptors:
- Rods: sensitive to light intensity (brightness)
- Cones: sensitive to different colors (concentrated in fovea centralis)
- Optic nerve: collects this information and sends it to the brain
Describe the aqueous humour:
- Fluid in anterior (front) chamber of eye
- Maintains cornea shape
- Provides oxygen and nutrients to lens and cornea
Describe the vitreous humour:
- Fluid in posterior (rear) chamber
- Helps maintain shape of eyeball
Describe how we focus our vision:
- Lens (along with cornea and humours) bends light entering the eye and focuses it on the back of the eye
- Note: image is revived in reverse and proceeded into the right orientation in the brain
How do we focus our vision on different objects?
- Ciliary muscles adjust shape of lens
- To focus on a distant object, muscles relax (and ligaments tighten) and lens flatten - lens is bent at a sharper angle
- To focus on a near object, the muscles contract (and ligaments relax) and the lens becomes round - light is bent at a wider angle
What are photoreceptors?
- Rods: very sensitive to light sensitivity
- Cones: sensitive to color
Describe rods:
- Make up 95% of photoreceptors
- Extremely sensitive to light
- Detect various shades of black and white
- Detect motion
- Responsible for peripheral vision
- More concentrated on outside edges of retina
Describe cones:
- Detect color
- Most are the fovea centrais
- Require intense light for stimulation (this is why we only see black and white when the light is low)
- Help us see detail (such as words on a page)
Describe the three types of cones:
- The three types of cones allow us to see different wavelengths of light
- Blue, red, green
- Using combinations of these cones allow for us to see many different colors
Describe the translation of light into nerve impulses:
- Rods contain rhodopsin cones contain photopsin, these are light absorbing pigments
- When a photoreceptor absorbs light, the pigment splits, which inhibits an inhibitory neurotransmitter (allowing a signal to be transmitted)
What is the nerve signal pathway?
- Rods and cones
- Biopolar nerve cells
- Ganglion nerve cells
- Optic nerve (formed by axons of ganglion cells)
How do impulses from the optic never get to the brain?
- Optic nerve
- Thalamus
- Signal from right side of eye goes to right occipital lobe
- Signal from left side of eye goes to left occipital lobe
- Result is image in stereo (binocular vision)
What are the divisions of the ear?
- Outer ear (pinna and auditory glands)
- Middle ear - tympanum (border), semicircular, canal and cochlea
- Fluid filled
Describe the pinna:
- Visible flap of the ear
- Focuses sound
Describe the auditory canal of the ear:
- 2.5cm long tube
- Leads from pinna to tympanum (ear drum)
- Amplifies sound waves
- Hair and ear wax prevent foreign materials from going dweller into the ear
Describe the tympanum of the ear:
- Ear drum
- Round, elastic structure
- Vibrates in response to sound waves
Describe the ossicles of the ear:
- Three small, interconnected bones (smallest bones in body)
- Use lever action to emphasize sound (small movement in one results in larger movement in next
- The three bones are malleus, incus and stapes (in order from external to internal ear)
Describe the oval window of the ear:
- Membrane covered opening to inner ear
- 15-30 times smaller than tympanum (so amplifies sound)
Describe the Eustachian tube of the ear:
- Connects middle ear to throat
- Allows air pressure to equalize (between middle ear and external environment
Describe the semi-circular canals and vestibule of the ear:
Contains sensors for balance
Describe the cochlea of the ear:
- Contains structures for hearing
- Mechanical energy (sound waves) converted into chemical energy
What are the parts of the cochlea?
- Organ of hearing, made of the following :
- Basilar membrane - mechchanoreceptors (hair cells) attached to the
- Stereocilla - fine projections of hair cells
- Tectorial membrane - stereocilla imbedded here
Describe the outer ear and hearing:
- Sound waves - fluctuations in air pressure
- Pinna collects sounds waves
- Auditory canal - amplifies sounds waves and directs them to the tympanum
Describe the middle ear and hearing:
- Sound waves push on tympanum, causing it to vibrate
- Vibrating tympanum pushes on malleus
- Malleus pushes against incus
- Incus pushes against stapes
- End of the stapes pushes on the oval window
Describe the inner ear and hearing:
- Vibration of oval window causes fluid of inner ear to vibrate (pressure waves)
- Basilar membrane in cochlea moves up and down
- Stereocilla bend against tectorial membrane
- Hair cells sense bending of stereocilla and send a message to the auditory nerve, which transmits a signal to the brain
Describe frequencies and hearing:
- High frequency sounds stimulate hair cells closest to the oval window
- Low frequency sounds stimulate hair
cells farthest from the oval window
Describe hearing loss:
- Results from damage to nerve, hair cell - nerve deafness
- Or damage to sound conduction system - conductive deafness
Describe the semicircular canals:
- Three fluid filled loops arranged in each of the three dimensions
- Responsible for rotational equilibrium
- As fluid in these canals moves, stereocilla inside canals are stimulated and send messages to the brain
- Sometimes when we stop moving, fluid is still moving which is why we feel dizzy
- Helps with balance
Describe the vestibule:
- Made of utricle and saccule
- Gravitational equilibrium
- Contains calcium carbonate granules (otoliths)
- Otoliths are in coupla (jelly) above hair cells
- When head moves back and forth gravity moves otoliths- movement stimulates the hair cells and sends information to the brain
- Helps us balance
